Modem digital networks are made to operate in a multimedia environment for transporting different types of data including pure data, i.e. files of alphanumeric characters, as well as data representing digitized and encoded voice, image, video signals etc. . . The network should, naturally ensure compliance with a number of requirements specific to each kind of such data traffic.
Different techniques have been developed for transporting data from one location to another, such as packet switching techniques where the data is arranged into packets. Those packets may either be a predefined fixed length, like in Asynchronous Transfer Mode (ATM), or be variable in length, like in a Packet Type Multiplexing (PTM) mode of operation currently used for transporting voice. The basic aim of both packet switching techniques, is to allow a statistical multiplexing of the different types of data onto transmission links to optimize, as much as possible, use of the available transmission bandwidth. Consequently, a large number of networks, both public and private, have been developed for transporting those data throughout the world.
On the other hand, the evolution of telecommunication technologies in general, and of packet switching networks in particular, is driven by many factors among which the technology evolution factor and the application factors are worth being emphasized.
As far as technologies are concerned, obviously considerable progress has been achieved recently with the maturing of new transmission media. High speed rates can now be sustained with very low error rates. High bandwidth can be turned into profit for long distance networks as well as for high rate local networks. Universal use of digital technologies appeared within both private and public telecommunication networks.
Due at least in part to the availability of these emerging technologies, many potential applications that were not possible in the past are now becoming accessible and attractive. In this environment, generic requirements are now expressed by the users, such as:
Improving old applications. Sub-second response times, which are achievable on low cost personal computers, have raised user expectations so that the lengthy wide area networks response times that were acceptable some years ago are today no longer tolerable. The user interface can be improved, for example, with fast response full screen applications. PA1 Enabling new applications. Emerging applications like graphic, image, video and multimedia processing are generating large volumes of traffic. These new applications, not considered feasible (or even thinkable) not too long ago, are now available and are generating an ever-increasing demand on bandwidth. PA1 Optimizing communication networks. There is a need for rationalizing the many disparate networks that major users have already implemented. Investments can be optimized by integrating heterogeneous traffic like voice, video, and data over the same transport facilities regardless of protocols. On the other hand, users want the opportunity to control their networking cost by choosing among the different price/performance options offered by the variety of vendors and carriers and to maximize their ability to take advantage of applications built on top of disparate underlying network technologies.
Accordingly, there has been an explosion in demand for high speed digital network facilities which is leading service providers to install core backbone networks to offer high speed data transportation facilities to large numbers of heterogeneous users' traffic, possibly through "access backbones". Bandwidth offered through such service providers should be transparent to users and should offer fairly large communication bandwidth at optimal cost.
Service providers are now running or expect to run large ATM core backbone systems for use by users needing to transport data traffic between distant locations throughout the world. Utilization of ATM core backbone systems makes particularly sense when the users traffic is multimedia in nature.
ATM networks are made to transport fixed length data packets, i.e,. 53 byte long packets having 5 bytes for a packet header and 48 bytes reserved to a data payload. Different techniques have been developed to convert variable length packets (PTM) into ATM-like fixed length packets that can then be transported throught the ATM core backbone. These techniques broadly include chopping the PTM packets into fixed length segments, assigning each segment a 5 byte long ATM-like header which enables forwarding the resulting fixed length packets into the ATM core network. Since most PTM variable length packets will not be a multiple of preassigned conventional length, the last constructed ATM packet from each PTM packet will typically have less than 48 bytes of data payload and will need padding bits. The padding bits carry no information and are considered overhead, which increases the bandwidth needed for a user's traffic.
For pure data providing fairly long and controllable packets, the added overhead is a relatively small portion of the overall traffic and thus may be ignored. This is far from being the case for multimedia traffic and more particularly for voice traffic generating randomly distributed relatively short PTM packets. For this kind of traffic, a method for transporting PTM originating data over an ATM network while minimizing overhead may result in significant savings for a customer leasing bandwidth in a service provider network.
Any method which minimizes the creation of overhead can be expected to be welcomed by both the ATM core backbone owner in a competitive service provider environment and by the user leasing bandwidth from such backbone owner.
The present invention focuses on solving the overhead problem created when padding bits are generated during the conversion of variable length data packets into fixed length ATM packets (or cells).